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Nitrogen Filled Tires? PDF Print E-mail
Written by Brian Dunning   
There is always someone out there looking for a way to squeeze a few extra dollars out of gullible consumers. Tire shops offering nitrogen filled tires are no exception.

Some racing cars use nitrogen in their tires, as do some aircraft and freight trucks. If the big boys are doing it, maybe it's a good idea, right? Well, it may be a good idea for them, but that doesn't mean that these benefits will transfer to your street car.
Compressed nitrogen doesn't expand and contract as much as compressed air due to temperature fluctuations, which makes it useful for racing with its extreme tire temperatures, but not nearly so useful for road cars. Some vendors claim better mileage with nitrogen in your tires. Increased tire pressure does indeed create less rolling resistance and thus higher efficiency, but since nitrogen expands less than air when your tires get hot on a long trip, you'll see less improvement with nitrogen. Only if your hot tire pressure is at the absolute max will you see mileage improvement using nitrogen, and then only when the tires are cold, and it's doubtful that this improvement would be enough to be measurable. Certainly any fuel savings would not come close to the extra expense of using nitrogen.

Aircraft and long-haul freight trucks fill with nitrogen because they keep their tires for several generations, retreading them whenever they get bald. Nitrogen oxidizes and deteriorates the inside of the tire less than air, useful when you keep large, expensive tire carcasses for a long time. Since you probably don't retread your street tires and keep them for multiple generations, this is another benefit that is lost on road cars. In any case, the atmospheric oxygen and ozone outside your tires is chewing away at the rubber, so it would be like wearing battle armor on half your body.

During a fuel crisis, vultures are always out there trying to appeal to your fears and offering miracle cures. While the benefits of nitrogen are real for specialized applications, there's usually no plausible justification of the extra expense with your average road car. Be skeptical.
Comments (3)Add Comment
written by Andres Villarreal, November 13, 2008
As far as I understand, the only component of air that makes the pressure in a tire change with temperature is water. You will get exactly the same variation in pressure with temperature changes, no matter what gas you use to fill your tires.

A far better way to eliminate this microscopic effect, where pressure decreases when water vapor in your tire condenses, a simple chamber where condensation separates from pressurized air is all that is needed, at a price of almost nothing.
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Ideal Gas
written by Kraig Knapp, November 13, 2008
I teach chemistry at the College of Southern Nevada and explain the gas laws every semester. Both nitrogen and oxygen behave like ideal gases under conditions found in tires. I defy anyone to be able to tell the difference based solely on pressure-temperature measurements. Although it is possible the racing teams use compressed nitrogen because of some woo-woo belief, it is more likely a safety issue. Compressed nitrogen is cheap and will not support combustion of petroleum products, unlike compressed air.
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written by PieterB, November 14, 2008
Costco inflates tires bought at its stores with nitrogen routinely at no charge. One advantage for the everyday driver is that nitrogen is a larger molecule than oxygen, and does not diffuse out through the tire as rapidly as plain old air. Consequently the pressure in your tires remains more stable, reducing wear and rolling resistance, which leads to both better tire life and better gas mileage. Like the old chicken soup joke goes, "It couldn't hoit!"

A co-worker of mine recently bought a new sportycar. One dealership -- which did not get his business -- adds a charge of $300 for nitrogen inflation, and you cannot opt out. FAIL.
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